The present invention relates to a thrust reverser for a turbojet engine, more particularly such a thrust reverser having a downstream baffle which deflects the turbojet engine gases and which is aerodynamically cooled.
Turbojet engines are, of course, well known in the art and typically have a hot gas exhaust duct, through which pass hot gases from the combustion chamber, surrounded by a generally annular cold gas duct through which comparatively cold air flows. Both exhaust ducts have downstream ends from which the gas flows emanate. The center, hot gas duct nozzle may be fitted with a mixer to permit mixing of the hot and cold gases issuing from the central duct and the annular duct.
Thrust reversers equipped on such turbojet engines typically comprise movable baffles located adjacent to the downstream ends of the hot and cold gas ducts which are movable into thrust reversing positions wherein the baffles contact the hot and cold gas flows to redirect them to generate reverse thrust. Contact between inner surfaces of the baffles, and the hot and cold gases cause high temperature spots to develop in the baffles. Heretofore, it has been necessary to fabricate the thrust reverser baffles from high temperature resistant, technically complex and costly materials in order to enable the baffles to withstand the high temperatures of the hot spots.
It has been noted that, during reverse thrust flow, the cold gas flow emanating from the generally annular cold flow duct to a certain extent encloses the hot gas flow emanating from the central, hot gas flow duct. This phenomenon protects certain portions of the thrust reverser baffles from the impact of the hot gases. However, the cold gas flow does not prevent certain portions of the baffle from developing high temperature hot spots.
Several solutions have been proposed to eliminate this problem. British Patent 1 542 642 discloses a thrust reverser in which a small wall is placed at an end of the thrust reverser in the gas ejection axis. This wall serves as an incident surface for the hot gas flow impact and serves to reverse the hot gas flow immediately after its exit from the engine nozzle. However, the baffle hot spots have been noted near the outermost limits of the baffles, not at the center of the thrust reverser. Thus, the aforementioned British patent has not achieved a complete solution to the problem.
U.S. Pat. No. 4,362,015 suggests increasing the ratio of the total pressures of the cold gas flow to the hot gas flow by placing movable flaps in the cold flow duct during thrust reversal operation. This concept uses a ratio of the total pressures of the cold gas flow to the hot gas flow of more than 1.2 and relies upon the fact that the cold gas flow entirely encloses the hot gas flow, thereby preventing the hot gas from coming into contact with the inner wall surface of the thrust reverser baffles. Normally, in a standard engine's thrust reversal mode, the ratio of pressures of the cold gas flow to the hot gas flow is approximately 1.1. Thus, the aforementioned U.S. patent requires a higher ratio of 1.2 in order to achieve its purposes. This entails the drawback of shifting or modifying the turbojet engine's operating characteristics and possibly encountering abrupt engine shutdown. Furthermore, should the overall pressure ratios be less than 1.2, the aforementioned patent provides ineffective insulation between the hot gas flow and the thrust reverser baffle.
U.S. Pat. No. 4,581,890 discloses a turbine engine which has controllable devices for inhibiting the device for mixing the hot and cold gas flows in order to protect the thrust reverser baffles from the hot gases.